Dryers are added as drying accelerators for drying inks to oxidative polymerization drying-type printing inks such as lithographic inks. The dryers generally used for the inks include metal salts (may be abbreviated as “metal carboxylates” hereinafter) of various carboxylic acids with heavy metals, such as cobalt, manganese, lead, iron, zinc, and the like. Among these metal carboxylates, cobalt metal carboxylates have been used as principal drying accelerators because they have excellent drying performance.
The cobalt metal carboxylates have excellent drying performance, but have the problem that when they are used in a large mount for more shortening the drying time, drying of ink surfaces very rapidly proceeds, and wrinkling and shrivering occur due to skinning, thereby causing difficulty in satisfying both the short drying time and the prevention of wrinkling and shrivering due to skinning. Therefore, as a method for shortening the drying time while preventing wrinkling and shrivering due to skinning, a drying accelerator using a cobalt metal soap in combination with bipyridyl is proposed (refer to, for example, Patent Literature 1). The drying accelerator prevents wrinkling and shrivering due to skinning and has a short drying time and high drying performance. However, use of the cobalt metal carboxylates has the problem that cobalt compounds are concerned above carcinogenicity because they are listed in Group 2B “Possibly carcinogenic to humans” in the list of carcinogenic risks of the International Agency for Research on Cancer, and that the cobalt metal carboxylates are expensive because metallic cobalt is a rare metal and thus suffers from unstable supply. There is thus demand for a drying accelerator having high drying performance using the cobalt metal soap in a smaller amount.
Therefore, as a drying accelerator having high drying performance using a smaller amount of the cobalt metal soap, a drying accelerator containing a cobalt metal soap, a manganese metal soap, and at least one aminoalcohol selected from diethanolamine, diethylethanolamine, dibutylethanolamine, and n-butyldiethanolamine is proposed (refer to, for example, Patent Literature 2). However, the cobalt metal soap is still used, and thus the problem of concern about carcinogenicity, unstable supply of the raw material, and high cost cannot be resolved.
There is thus demand for a dryer (drying accelerator) which can further decrease the amount of cobalt metal soap used and has the high drying performance of having a short drying time and being capable of preventing wrinkling and shrivering due to skinning.